The present invention relates to a system for transmitting an electrical signal along a drill string or other pipe string while it is in the borehole of a well. More particularly, the invention relates to an information telemetering drill string that can be made and used without expensive specialized pipe manufacturing, or drill string operating techniques, or precautions.
The desirability of transmitting an electrical signal along a drill string was recognized over 40 years ago and numerous methods and apparatus have been proposed. Typical prior proposals have required specially-constructed drill pipe sections such as those described in U.S. Pat. No. 2,178,931, or have required complex fabrication and assembly such as continuously brazing or otherwise attaching a conduit inside the pipe joints such as those described in U.S. Pat. Nos. 2,096,359; 2,197,392; 3,170,137; or 3,253,245. The mountings shown in U.S. Pat. No. 2,531,120 for an insulated electrical conductor comprises a straight conduit, extending along the length of the pipe, and joined at each end to a passageway formed in the ends of the pipe. No mention is made of sealing the tube at its ends and no continuous or intermittent attachment of the tube to the pipe is disclosed. It can be shown that an unattached tube or conduit will preclude running wireline tools through the pipe.
In the drill string described in U.S. Pat. No. 3,696,332, the pipe joint electrical connectors comprise insulated metal rings mounted in grooves located between the inner and outer portions of mating sealing shoulders in the pipe joints. This is advantageous in isolating the connectors and associated insulating materials from fluid in or around the drill string (by the metal-to-metal joining of the pipe joint sealing shoulders) when the pipe sections are interconnected. U.S. Pat. No. 3,696,332 also discloses a conduit that extends through the pipe and joins at each end to passageways formed in the pipe. The conduit is not sealed to the pipe, nor are means for attaching the conduit to the pipe disclosed.